I recommend a more experienced doctor.

Just kidding.  I know it's a typo.  ;-)

Hives are definitely a sign of allergic reaction and not scarlet fever.
From what you've described, I would put the amoxicillin high on the list of
suspects.

I doubt that holding off on the amoxicillin for another 12-24 hours will
matter much.  I would do so until you can get in to see the doc.

A scarlatiniform rash is a fine, dry, bumpy, red rash with a
"sandpaper" texture with a characteristic distribution. It does not
come and go, it is usually not itchy, and does not respond to
Benadryl. Hives, however, are variably sized and shaped rashed, red
areas as descrbied by Dr. Harris that do come and go, usually itch,
and can completely disappear temporarily with Benadryl.

Here's my guess as to what most likely happened (assuming she had no
other symptoms prior to or concurrent with the sore throat and fever):

Child gets a virus infection, develops the prodrome of sore throat,
and subsequent fever. Child is seen and the eardrum is "red" and thus
is diagnosed with an ear infection, even though the child did not have
the typical antecedent cold symptoms nor an ear ache. The child is
then treated with an antibiotic for a viral illness.

Then, as is common in children, the virus causes hives. (I would
disagree with Mr. Gregory that hives "are definitely a sign of
allergic reaction".) Some diagnostic confusion ensues, and the
antibiotic is continued. The hives wax and wane as they are wont to
do.

Or, perhaps it truly is an amoxicillin allergy. We'll likely never
know.

Side note: Some happy news is that because these days a lot fewer kids
are treated with an antibiotic at the beginning of a viral illness
than were just a few decades ago, we are growing a new generation of
Americans who are not afflicted with epidemic "penicillin allergy",
since it seems that all the viral rashes in children of the 1960's and
1970's occurred while they were taking antibiotics, and they were thus
branded so. It's no wonder why, consistently in several studies, only
about 4% of adults who think they are "allergic" to penicillin
actually are.

What would I do with this child if she presented to my office? As Dr.
Harris pointed out, antibiotics don't really do much to modify the
course of streptococcal pharyngitis, which is largely a self-limited
illness (a fact few parents know). However, the main reason for
treating strep throat with antibiotics is to prevent rheumatic fever,
which was the most common cause of acquired heart disease in children
and young adults prior to the antibiotic era. (Would anyone like to
guess what has become the number one cause now?) If the only history I
had was fever and sore throat, but a strep swab was obtained only
after starting antibiotics, there is a small but real risk of
rheumatic fever from discontinuing antibiotics. One is thus obligated
to complete a treatment for strep throat. With the presence of hives,
however, which could be from the amoxicillin, the risk of continuing
amoxicillin is producing anaphylaxis. I would thus switch her to
either azithromycin or cephalexin. She would then get better, the
hives would go away, we would label her chart "allergic to
amoxicillin" and we'd never really know if she really is allergic to
amoxicillin or if she had strep throat or not. But at least she'd be
all better.

As for stopping the antibiotics until she can be seen again: Treatment
of strep throat should commence within 10 days of onset to effectively
prevent rheumatic fever. There is usually plenty of time. As I often
say, there are very few good reasons to take an antiobiotic, but many
good reasons not to.

PF

I definitely defer to the more knowledgeable answering your question.
However, I am under the impression that Scarlet Fever is essentially
extreme strep pharyngitis (strep throat).  Rash is common with Strep, or
especially Scarlet Fever.  Now, I agree, hives (as described before) would
be indicative of an allergic reaction, likely to the amoxicillin.  But if
the rash is not hives, then I would cautiously assume that the rash is a
result of the scarlet fever.  However, keep an eye out for breathing
difficulties, etc. that would indicate an allergic reaction.

I hope she feels better soon.  I just got over strep throat, and it's not a
pleasant experience.  In fact the first doctor I saw (I live in Juneau,
Alaska) decided I had a stomach virus, despite the fact that I had EVERY
classic damn symptom of strep.  Didn't do a culture, nothing.  By the next
morning I was so bad off, I wound up getting IV fluids, steroids, and anti-
inflammatories. ARGH.